docs: def ToPhotlam(self, wave, flux, area=None):
          """Convert to ``photlam``.
  
          .. math::
  
              \\textnormal{photlam} = \\frac{\\textnormal{counts}}{\\delta \\lambda \\; \\times \\; \\textnormal{area}}
  
          where :math:`\\delta \\lambda` represent bin widths derived from
          :func:`~pysynphot.binning.calculate_bin_edges` and
          :func:`~pysynphot.binning.calculate_bin_widths`, using the input
          wavelength values as bin centers.
  
          Parameters
          ----------
          wave, flux : number or array_like
              Wavelength and flux values to be used for conversion.
  
          area : number or `None`
              Telescope collecting area. If not given, default value from
              :ref:`pysynphot-refdata` is used.
  
          Returns
          -------
          result : number or array_like
              Converted values.
  
          """
          area = area if area else refs.PRIMARY_AREA
          bin_widths = \
              binning.calculate_bin_widths(binning.calculate_bin_edges(wave))
  
          return flux / (bin_widths * area)